Ammonia Purge Near Miss

Jason Clarke, Gulf Power Co.

• Four generating units

2 - 82 MW

1 - 320 MW

1 - 500 MW

• All four units run through a common scrubber

• The two large units utilize SCR technology and

have anhydrous ammonia injection systems

Plant Crist Overview

• 11/5/2014

–SCR System Owner put in a Clearance request to

replace multiple pressure relief valves on the

ammonia system according to maintenance strategy

schedule.

Incident Overview

• 11/10/2014

–Plant Operations discovered a small ammonia leak

during the nightshift.

–Operations barricaded the area from a safe distance

and placed a clearance on the system thereby

isolating ammonia.

Incident Overview

• 11/11/2014 (Dayshift)

–With the ammonia system out of service and no

pressure on the system, the location of the small

leak could not be determined.

–The various pressure relief valve replacement job

was completed as planned.

–As the system was returned to service, no leak was

detected.

Incident Overview

• 11/11/2014 (Nightshift)

–The same crew working the previous night noticed

that the leak reappeared.

Incident Overview

• Subsequently, the following events occurred that

same night:

–The operations team leader contacted the team

leader on call, which informed him to contact the

manager on call.

–The manager on call was notified and instructed the

operations team leader to contact the emergency

response contractor to make the necessary repairs.

Incident Overview

• 2130 hours

–The contractor arrived on plant site and made

contact with the operations team leader and

proceeded to the leak site. It was determined that

the leak was coming from a hose that was located

on the grating. This hose was attached to a fitting

that was used to purge ammonia from the system

prior to performing needed work.

Incident Overview

• The perceived lack of necessary parts did not

allow the contractor to make the immediate

repairs. However, the contractor did temporarily

mitigate the situation by placing the hose in a

drum of water.

Incident Overview

Incident Overview

Drum of

water

Hose

Valve

• 2300 hours

–Contractor left the plant site.

• Leak was determined to be mitigated and system left

in service.

• 2330 hours

– Plant operations visually determined that the

ammonia leak had reappeared

• Calls placed to plant environmental group

Incident Overview

• The information conveyed from environmental

compliance was that the ammonia system could

be isolated and left out of service until the

morning for protection of personnel.

– Lastly, it was suggested to contact the system

owner to inform him of the current situation.

Incident Overview

• 2345 hours

– Operations team leader made contact with the

system owner.

• The system owner informed the team leader that the

parts necessary for repair were on plant site.

Incident Overview

• The system owner also confirmed that a C&R

technician, which was working on plant site that

night, was capable of making the repairs.

Incident Overview

• 0120 hours

– C&R employee approached the area of the leak and found

that the hose was no longer vented into the drum of water.

Instead, it had come out of the water and was located on

the top of the drum.

Incident Overview

Incident Overview

Drum of

water

Hose

Valve

• 0130

– The C&R employee placed the hose back into the drum of

water, unaware that a small amount of liquid ammonia was

in the hose.

Consequently, the mixture of ammonia and water reacted

causing a plume of vapor.

Incident Overview

Latent Conditions • Bleed off hose was never removed from equipment

from prior outage.

• Hose discharge elevation allowed accumulation of

liquid NH3.

• Recognition for potential of liquid ammonia

accumulation in the hose.

• Lack of awareness to level of reaction.

Incident Overview

Latent Conditions • Specialized contractor successfully performed same

task earlier in the night.

• Specialized contractor successfully performed same

task with only respirator as task specific PPE.

• Time of event – event occurred on night shift.

• Infrequent task

Incident Overview

Latent Conditions • Repair expectations

• Criticality not identified: Identification and repair of leak

on Tuesday day shift

• Condition report not generated upon discovery of the

initial ammonia leak.

• Limited visibility

Incident Overview

Latent Conditions • T.L. had multiple concerns (Distractive Environment )

• Inaccurate Risk Versus Reward Assessment

• Hose did not appear secured to barrel of water by

contractor.

• Operations team leader was not aware of onsite

material.

Incident Overview

Root Causes • Hose used for purging ammonia left in place from

previous outage

• Ammonia valve leaking by

• Chain of command protocol/experience

Incident Overview

Corrective Actions • Purge checklist procedure for ammonia system and

miscellaneous ammonia purging.

• Inspect and repair leaking valve

• Perform broadness review of other similar valves in the

system

Incident Overview

Corrective Actions • Technical evaluation for upgraded purging

equipment/system

• Supervisors and managers, in discussion of this RCA

with their employees, are to emphasize the importance

of full circle communication (chain of command and

subject matter experts).

• Technical Evaluation: Event Notification to Generation

Fleet for review

Incident Overview

Incident Overview

Purge

flange

Valve

Questions?

Incident Overview